Optical receiver for multicarrier modulation in short-reach communication

Abstract

A high-linearity optical receiver with background-light-AGC for high PAPR signals is presented. The integrated BiCMOS optical receiver consists of a TIA with AGC, a linear amplifier and a line driver. The receiver THD is 1.7% and the third-order intermodulation is 50 dBc at 20 MHz and at an input optical power of 23.5 dBm. The thirdorder intermodulation decreases to 40 dBc at 100 MHz.Introduction: Short-range optical data transmission is attracting increasing interest in industry automation, in-car communication, and home networking. Polymer optical fibre (POF) represents an alternative to silica fibre for short-range communication and offers particular advantages. However, owing to its large numerical aperture of 0.5 and large core diameter the bandwidth of SI-POF is limited to 50 MHz/ 100 m. By use of multicarrier modulation schemes like OFDM such bandwidth limitations can be overcome. OFDM is seen as a promising technology for low-cost gigabit transmission over SI-POF [1].A major problem of OFDM is that the multicarrier signals usually have large envelope fluctuation. This means that the peak-to-average power ratio (PAPR) of multicarrier signals can be high. These large peaks increase the amount of intermodulation distortion (IMD), resulting in an increase in error rate.A high-linearity receiver with AGC is required for OFDM to reduce IMD. AGC adjusts the gain of the amplifiers to obtain the desired output signal strength. In conventional AGCs the signal amplitude is typically estimated using a peak detector. This adequately works for signal amplitudes with fixed PAPR such as sinusoids, but is unreliable for high-PAPR signals. These issues excluded the use of a conventional AGC with OFDM [2]. The wireless local area network receiver presented in [2] implemented an AGC, which uses RMS detection. This was found to be adequate for estimating the OFDM amplitude by integrating the duration of a training symbol.In this Letter we present an integrated linear optical receiver consisting of a TIA with AGC followed by an amplifier and a line driver. Additionally two main control loops are present, one for backgroundlight (BGL) cancellation and one for the gain control. The speciality of this linear optical receiver is that the gain is only controlled by BGL, which is always present in optical transmission systems owing to laser diode biasing above the threshold (limited extinction ratio). The presented BGL-AGC can achieve better linearity than peak-detecting AGC especially for pulsed signals or more general signals with high PAPR where the pulse repetition rate is low. When peak detection is used with this kind of signals, large storage capacitors would be necessary to store the peak value. Additionally, large capacitors cannot easily be charged very quickly and accurately. We do not need these large capacitors with the BGL-AGC.Nearly all previous attempts to design a linear optical receiver for short-range communication include only simulation results. No measurements have been presented to verify the optical receiver ...

170Mb/s multilevel transmission over 115m standard step-index plastic optical fiber using an integrated optical receiver

“…The THD of the receiver is 1.7% and the third-order intermodulation is −50 dBc at 20 MHz and at an input optical power of −3.5 dBm. The optical receiver has a sensitivity of −31 dBm (BER =10 −9 ) at 250 Mb/s for a binary signal and a sensitivity of −25 dBm at 500 Mb/s with fourlevel pulse amplitude modulation [4,6]. The integration of photodiode with the amplifiers improves the performance by reducing lead capacitance and susceptibility to interference, thereby giving higher speed and lower noise.…”

250 Mbit/s over 100 m SI-POF with RCLED source using integrated post-equaliser

“…300 Mbit/s over a 50 m-long POF link using a commercial RCLED at BER 1.9 × 10 23 was presented in [5] using carrier-less amplitude phase modulation. There is a need for more circuits at the transmitter to generate these complex modulation formats and also at the receiver to decode these complex signals to binary [6,7]. Post-equalisation techniques can help to solve the problem of limited bandwidth of the SI-POF [8].…”